PS7516. Description. Features. Applications. Pin Assignments. Functional Pin Description

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1 Description The PS756 is a high efficiency, fixed frequency 550KHz, current mode PWM boost DC/DC converter which could operate battery such as input voltage down to.9.. The converter output voltage can be adjusted to a maximum of 5.25 by an external resistor divider. Besides the converter includes a 0.08Ω N-channel MOSFET switch and 0.2Ω P-channel synchronous rectifier. So no external Schottky diode is required and could get better efficiency near 9%. 96%. The converter is based on a fixed frequency, current mode, pulse-width-modulation PWM controller that goes automatically into PSM mode at light load. When converter operation into discontinuous mode, the internal anti-ringing switch will reduce interference and radiated electromagnetic energy. The PS756 is available in a space-saving SOT-2-6 package for portable application. Features High Efficiency up to 96% Low R DS (ON) Integrated Power MOSFET NMOS 80mΩ / PMOS20mΩ Wide Input oltage Range:.9 to 5.5 Fixed 550KHz Switching Frequency Low-Power Mode for Light Load Conditions ±2.0% oltage Reference Accuracy PMOS Current Limit for Short Circuit Protection Low Quiescent Current Output Ripple under 200m. (Scope Full Bandwidth) Fast Transient Response Built-In Soft Start Function Over-Temperature Protection with Auto Recovery Output Overvoltage Protection Space-Saving SOT-2-6 Package Applications Portable Power Bank Wireless Equipment Handheld Instrument GPS Receiver (When in = 4.2) Pin Assignments SOT IN OUT EN LX FB Figure. Pin Assignment of PS756 Functional Pin Description Pin Name Pin No. Pin Function LX Power Switching Connection. Connect LX to the inductor and output rectifier. 2 Ground Pin. FB oltage Feedback Input Pin. EN 4 Logic Controlled Shutdown Input. OUT 5 Output of the Synchronous Rectifier. IN IN 6 Power Supply Input Pin.

2 . Block Diagram IN LX EN On/Off Control ANTI-RING PMOS OUT NMOS Body-Diode Switch PFM Control OSC OP ULO PWM Control Logic OTP Isense/Current Limit Slope Comp. COMP Anti-Reverse Comparator Error Amp Bandgap Reference FB IN Figure. Block Diagram of PS756 2

3 Typical Application Circuit IN 2.5 to 5.5 L 0μH OUT 5/A C C2 0μF 0.μF 6 C4, C6 IN LX 0.μF PS OUT C, C5 22μF R 525K ON 4 EN FB R2 00K OFF Figure 2. Typical Application Circuit Absolute Maximum Ratings (Note ) Supply oltage IN to +6.5 LX oltage LX to +6.5 All Other Pins oltage to +6.5 Maximum Junction Temperature (T J ) C Storage Temperature (T S ) C to +50 C Lead Temperature (Soldering, 0sec.) C Package Thermal Resistance (θ JA ) SOT C/W Package Thermal Resistance (θ JC ) SOT C/W Note :Stresses beyond this listed under Absolute Maximum Ratings" may cause permanent damage to the device. Recommended Operating Conditions Supply oltage IN to +5.5 Output oltage Range up to Operation Temperature Range C to +85 C

4 PS756 85T Electrical Characteristics 85T (IN=., TA=25 C, unless otherwise specified.) Parameter IN Input Supply oltage Symbol Conditions IN Min Typ..9. Max Unit 5.5 Input ULO Threshold IN Rising.85 Under oltage Lockout Threshold Hysteresis IN Falling μa Supply Supply Current Current (Switching) Feedback oltage FB 2.5 IN High-Side PMOSFET RDS(ON) 20 mω Low-Side NMOSFET RDS(ON) 80 mω High-Side MOSFET Leakage Current ILX(leak) Low-Side MOSFET Leakage Current Oscillation Frequency LX=5.5, OUT=0 0 μa LX=5.5 0 μa 650 KHz FOSC 550 Switch Current Limit IN=. Short Circuit Trip Point Monitored FB voltage 0. Short Circuit Current Limit IN =. 50 ma IN=. 90 % Maximum Duty Cycle DMAX Line Regulation IN=2.5 to 5.5, IOUT=00mA Load Regulation IOUT=0A to A 2.5 OP Threshold oltage on OUT Pin OP Threshold Hysteresis Internal Soft-Start Time EN (L) EN Input High oltage EN (H) EN Input Current IEN % m Thermal Shutdown Threshold (Note 2) TSD.4 IN=. % 0.5 EN Input Low oltage Thermal Shutdown Hysteresis A ms μa 50 C 0 C Note 2 Not production tested. 4

5 Application Information Controller Circuit The device is based on a current-mode control topology and uses a constant frequency pulse-width modulator to regulate the output voltage. The controller limits the current through the power switch on a pulse by pulse basis. The current sensing circuit is integrated in the device; therefore, no additional components are required. Due to the nature of the boost converter topology used here, the peak switch current is the same as the peak inductor current, which will be limited by the integrated current limiting circuits under normal operating conditions. Synchronous Rectifier The device integrates an N-channel and a P- channel MOSFET transistor to realize a synchronous rectifier. There is no additional Schottky diode required. Because the device uses a integrated low R DS(ON) PMOS switch for rectification, the power conversion efficiency reaches 9%. A special circuit is applied to disconnect the load from the input during shutdown of the converter. In conventional synchronous rectifier circuits, the backgate diode of the high-side PMOS is forward biased in shutdown and allows current flowing from the battery to the output. This device, however, uses a special circuit to disconnect the backgate diode of the high-side PMOS and so, disconnects the output circuitry from the source when the regulator is not enabled (EN=low). PSM Mode The PS756 is designed for high efficiency over wide output current range. Even at light load, the efficiency stays high because the switching losses of the converter are minimized by effectively reducing the switching frequency. The controller will enter a power saving mode if certain conditions are met. In this mode, the controller only switches on the transistor if the output voltage trips below a set threshold voltage. It ramps up the output voltage with one or several pulses, and goes again into PSM mode once the output voltage exceeds a set threshold voltage. Device Enable The device will be shut down when EN is set to. In this mode, the regulator stops switching, all internal control circuitry including the low-battery comparator will be switched off, and the load will be disconnected from the input (as described in above synchronous rectifier section). This also means that the output voltage may drop below the input voltage during shutdown. The device is put into operation when EN is set high. During start-up of the converter, the duty cycle is limited in order to avoid high peak currents drawn from the battery. The limit is set internally by the current limit circuit. Anti-Ringing Switch The device integrates a circuit which removes the ringing that typically appears on the SW node when the converter enters the discontinuous current mode. In this case, the current through the inductor ramps to zero and the integrated PMOS switch turns off to prevent a reverse current from the output capacitors back to the battery. Due to remaining energy that is stored in parasitic components of the semiconductors and the inductor, a ringing on the SW pin is induced. The integrated anti-ringing switch clamps this voltage internally to IN ; therefore, dampens this ringing. Adjustable Output oltage The accuracy of the output voltage is determined by the accuracy of the internal voltage reference, the controller topology, and the accuracy of the external resistor. The reference voltage has an accuracy of ± 2%. The controller switches between fixed frequency and PSM mode, depending on load current. The tolerance of the resistors in the feedback divider determines the total system accuracy. Design Procedure The PS756 boost converter family is intended for systems that are powered by a single-cell Ion battery with a typical terminal voltage between to

6 Application Information (Continued) () Programming the Output oltage The output voltage of the PS756 can be adjusted with an external resistor divider. The typical value of the voltage on the FB pin is 800m in fixed frequency operation. The maximum allowed value for the output voltage is 5.5. The current through the resistive divider should be about 00 times greater than the current into the FB pin. The typical current into the FB pin is 0.0µA, and the voltage across R2 is typically 800m. Based on those two values, the recommended value for R2 is in the range of 800kΩ in order to set the divider current at µa. From that, the value of resistor R, depending on the needed output voltage ( O ), can be calculated using Equation. R R2 O T F - 800kΩ O T 800m -..() (2) Inductor Selection A boost converter normally requires two main passive components for storing energy during the conversion. A boost inductor is required and a storage capacitor at the output. To select the boost inductor, it is recommended to keep the possible peak inductor current below the current limit threshold of the power switch in the chosen configuration. The second parameter for choosing the inductor is the desired current ripple in the inductor. Normally, it is advisable to work with a ripple of less than 20% of the average inductor current. A smaller ripple reduces the magnetic hysteresis losses in the inductor, as well as output voltage ripple and EMI. But in the same way, regulation time at load changes rises. In addition, a larger inductor increases the total system cost. With those parameters, it is possible to calculate the value for the inductor by using Equation 2. () Capacitor Selection The major parameter necessary to define the output capacitor is the maximum allowed output voltage ripple of the converter. This ripple is determined by two parameters of the capacitor, the capacitance and the ESR. It is possible to calculate the minimum capacitance needed for the defined ripple, supposing that the ESR is zero, by using Equation. M N O T O T - N O T..() Parameter f is the switching frequency and is the maximum allowed ripple. The total ripple is larger due to the ESR of the output capacitor. This additional component of the ripple can be calculated using Equation 4. ESR O T R ESR..(4) The total ripple is the sum of the ripple caused by the capacitance and the ripple caused by the ESR of the capacitor. It is possible to improve the design by enlarging the capacitor or using smaller capacitors in parallel to reduce the ESR or by using better capacitors with lower ESR, like ceramics. Tradeoffs must be made between performance and costs of the converter circuit. A 0µF input capacitor is recommended to improve transient behavior of the regulator. A ceramic or tantalum capacitor with a 00nF in parallel placed close to the IC is recommended. N O T - N O T..(2) Parameter is the switching requency and Δ L is the ripple current in the inductor, i.e, 20% x I L. With this calculated value and currents, it is possible to choose a suitable inductor. Care must be taken that load transients and losses in the circuit can lead to higher currents. Also, the losses in the inductor caused by magnetic hysteresis losses and copper losses are a major parameter for total circuit efficiency. 6

7 . Application Information (Continued) Layout Considerations As for all switching power supplies, the layout is an important step in the design, especially at high peak currents and high switching frequencies. If the layout is not carefully done, the regulator could show stability problems as well as EMI problems. Therefore, use wide and short traces for the main current path as indicated in bold in Figure 4. The input capacitor, output capacitor and the inductor should be placed as close to the IC as possible. Use a common ground node as shown in Figure 4 to minimize the effects of ground noise. The feedback divider should be placed as close to the IC as possible. IN OUT C C C4 C6 C C5 L LX 2 R2 R Figure 4. Layout Diagram 7

8 Outline Information SOT-2-6 Package (Unit: mm) SYMBOLS UNIT Carrier Dimensions DIMENSION IN MILLIMETER MIN MAX A A A B D E E e e L Note:Followed From JEDEC MO-78-C. 8